Magnetoelectric transducer for measurement of velocity and related values



June 19, 1951 s, E. DAWSON 2,557,080

MAGNETOELECTRIC TRANSDUCER FOR MEASUREMENT OF VELOCITY AND RELATED VALUES Filed Sept. 16, 1948 '5 amual Edward Claws:

BY NA.

' ATTORNEY.

Patented June 19, 1951 MAGNE'EQEHJECTRHC MEASUREMENT OF VELOCITY RE- LATEX) VALUES TRANSDUCER EFGR Samuel Edward Dawson, Fairway Hills, Md. ltppiication September 16, 1948, Serial No. 49,637

6 Claims. (6i. 177-352) ,(Granted under the act of March 3, 1883, as amended Aprii 30, 1928; 370 0. G. 757) The invention relates to improvements in magneto-electric devices and more particularly to an improved instrument of the magneto-electric transducer type suitable for use in the detection and measurement of vibratory or shock-excited velocities and their time derivatives or integrals. By reversing its operation, the device can also be used as a vibration generator to produce uniform or harmonic motion. I i

The primary object of the invention is the provision of a magneto-electric device having an improved magnetic circuit including portions wherein objectionable leakage flux is controlled or eliminated so that the response of the device to all types of vibrations may be more accurately interpreted.

The invention also aims to provide a magnetoelectric device of the character described which may be used in either a vertical or a horizontal position, which is relatively strong and light so as to withstand extremely high longitudinal and transverse acceleration forces, which has a friable magnetic element so mounted as to withstand shock, and which is completely submersible.

Other objects and many of the attendant advantages of this invention will be readily appre- 4 of illustration shows only a preferred embodimentof the invention, the numeral I generally designates the improved magneto-electric device including a cylindrical case ll formed of beryllium copper and adapted to be rigidly fastened at its basal end l2 to a movable body, as by feet l3.

Releasably fastened to the opposite end of the case as by screws 14 and engaging a suitable sealing ring I5 is a waterproof cover I6 provided with a packing I! through which cable l8 extends.

Disposed within the case is a cylindrical support 89 formed of beryllium copper and held in inwardlyspaced coaxial alignment with-the case as by annular flanges 20, 2|. These flanges engage the inside of the case and at least one flange 2| is connected thereto as by screw threads 22.

Reciprocably slidable in the cylindrical support I9 is a seismic element 23 preferably including a magnetizing element comprising an axiallydisposed permanently-magnetic bar 24 formed ,of Alnico V. Obviously an electromagnet could be used instead of the permanently-magnetic bar 2&

ifdesired. Resiliently supported for movement,

longitudinally of the case M, as by opposed coil springs 25, 28 and screws 21, is a magnetizable cylindrical shell 28 provided at one end with an inturned annular flange 29 and at its opposite end with an annular coaxially-disposed socket portion 39 fitted on one end of the bar 24. By properly setting the screws 2?, the tension of the opposed springs 25, 26 may be so adjusted that the seismic element 23 will normally rest in a predetermined central position in the support 89 when the case M is horizontally mounted. In order to compensate for the weight of the seismic element 23 when the case is vertically mounted, the screws 2i may be so adjusted that the tension of the upper or lifting springs 25 will be greater than that of the lower springs 26 whereby the seismic element may becaused to float centrally of the case. Fitted on the other end of the bar 24 is the annular coaxially-disposed socket portion 3! of a disc 32 terminating in a circumferential edge closely spaced within the flange 29 so as to form an annular airgap 33. The shell 28 and disc 32 are made of magnetic metal such as Swedish charcoal iron so as to form a magnetic circuit for the bar it including the airgap 33. Encircling the bar 25 is a tension sleeve 34 formed of a nonmagnetic material such as beryllium copper and screw-threadedly connected at its ends to the annular socket portions 30, 31 so as to hold the Alnico bar in compression. Even though Alnico is a material that tends to go to pieces under shock, holding the bar in compression enables it to withstand accelerations in excess of 4000 G.

Afiixed to the support i9 as by screws 35 is a cylindrical Micarta form 36 supporting a coil 31 that extends through the airgap 33 and terminates in a zone 38 within the shell adjacent the airgap 33. The length of the coil 31 should be greater than the width of the airgap and the stroke of the seismic element should be limited as by bumpers 39, 40 so that the free end of the coil will always be beyond the gap. The cable 18 is connected to the ends El, 42 of the coil so as to transmit the electrical output thereof to any suitable indicator or recorder (not shown). The zone 38 adjacent the airgap 33 normally would be subjected to leakage flux from the previously mentioned magnetic circuit. Consequently the coil 31 upon relative movement of the case II and seismic element 23 would normally out not only the entire airgap flux but also a variable quantity of leakage flux in zone 38. Thus the signal generated in the coil 31 would depend not 3 only on its movement relativeto the'seismic element but also on its position in the zone 38.

In order to eliminate this objectionable leakage flux in the path of travel of the coil 31 relative to the seismic element 23, the magnetic circuit is provided with a shunt 43 which comprises an internal annular rib 44 carrying a cylindrical flange 45. This flange is coaxially disposed Withe in the shell andextends through the flux leakage zone 38 alongsidethe path of travel of coil 31 and at the side thereof opposite'the shell, then terminating in an internally-thickened marginal edge 46 spaced from the disc 32 to form an airgap 41. The internally-thickened marginal edge '46 serves to direct the shunt flux inwardly and away from the coil. The non-magnetic sleeve 34 is provided with radial flanges 4B, 49 engaging and firmly reinforcingithe shell 28 and flange 45 respectively.

The magnetic shunt 43 should be so locatedand proportioned relative to the-main magneticv circuit that the magnetomotive force gradient is the same at'opposit'e points along the shunt and the main magnetic circuit. Leakage flux across the compartmenttfl defined by theflange 45 and shell 23 will be eliminated by equalizing the magnetic potentials at corresponding points on op- .posite sides thereof. v

There'will of course .be a loss of efllciency due' todiversion of some of the flux rromthe main order to minimize the loss ofiefliiciency, the shuntv path should be made relatively and the shunt gap 41 increased until conditions of equal used, it is considered necessaryto adjust the reluctance of the shunt path for optimum results. To determine the exact dimensions of the magnetic parts by calculation would ordinarily be too complicated and not practical. Although rough adjustments of the shunt path reluctance may be vanometer search coil (not shown) moving back and forth in the flux leakage zone gives no indi- 5 cation of magnetism. The main gap 33 should.

be as small as possible formaximum eficiency.

The shunt path may be designed for a flux diversion of about 25% so thatthere will be a relatively small ratio of by-pass fiux to useful flux. 5

II and seismic element 23 will be generated. In-

asmuch as the free end portion of the coil 31 always operates in the leakage-free compartment 50 and an intermediate portion of the coil 31 al- 65 ways cuts the totalfiux across the airgap 33, the

, magnitude of the signal generated will'be'inde pendent of the position of the coil 31 relative to the gap 33. It is therefore evident thatthe device III is particularly well adapted for use as a detector of vibratory or shock-excited movements of all types, harmonic or non-harmonic, where the accurate measurementsof such movements is important. i

Obviously many modifications'and variations of magnetic gradient exist at corresponding points on' the main and shunt paths. Inasmuch as the design dimensions of the magnetic circuit and shunt depend on the permeability of the material the prese'ntinvention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise 5 than as specifically described.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

' I claim:

1. In a magneto-electricfdevice of the character described, almagnetic circuit including an airgap and having a flux leakage zone adjacent the airgap, a coil, means supporting said coil for 'said coil in a position to cut the flux in said air gap transversely,.said coil and supporting means being so constructed and arranged as to keep a portion of said coil always fully across said air gap during movement of said coil, whereby the 5 flux inisaid airgap and a variable portion of the leakage flux zone is cut by s'aid'coil during travel of said coil, and a magnetic, shunt comprising a magnetic sleeve longitudinally co-axial with said coil diverting leakage flux around an end of the path of travel of said coil, whereby flux leakage v in the path of travel of said coil is eliminated.

2. In a magneto-electric device of the char acter described, a. magnetic circuit including a pair of spaced members providing an airgap and a flux leakage zone adjacent the airgap, a coil having a portion about a, first of said members and movable relative to the spaced members, said movement of-said coil being in a path como prising portions of said airgap and flux leakage zone, whereby the flux in said airgap and a variable portion of the leakage flux zone is cut, and a magnetic shunt magnetically intimately associated with the other member and having a portion extending between said coil and said first Y member for diverting flux tending to as from made by variation of the shell thickness, the p final adjustment generally should be made by varying the shunt gap width until a ballistic galsaid first member at one side of the path of travel of said coil to the other member at the other side 'of said path, the reluctances of said shunt and said other member being so chosen that the leakof flux therebetween is substantially eliminated.

3. In a magneto-electric device oithe character described, a case, a seismic element resiliently supported in the case, said element comprising a permanently magnetic bar, first and sec- 5 0nd magnetic members conducting flux from opsite end portions of the bar, said members defining an air gap and a flux leakage zone adjacent said gap, a coil supported by the case for movement relative to said gap whereby the flux in said gap and a variable portion of said'leakage flux is cut, and a magnetic shunt diverting flux from one of said membersat one side of the path of travel of said coil to the opposite side of said path, the reluctances of said shunt and said member being so'chosen that the leakage of flux therebetween is substantially eliminated.

4-. A magneto electric device of the character described comprising a magnetic circuit includmg a magnetizing element and a magnetizable shell spaced to provide an airgap and a flux leakage zone adjacent said airgap; said magnetizing element comprising a bar; a non-magnetic sleeve encircling said bar; a pair of end-members pressing on the endsof said bar; said sleeve being 5 7 connected to said end-members so asto hold said bar in compression; a coil movable in a path including said airgap and a portion of said flux leakage zone; and a magnetic shunt magnetically intimately associated with said shell andextending between said element and the portion of said coil in said flux leakage zone and magnetically shunting a part of said magnetic circuit for divertlng flux from said portion of said flux leakage zone; the reluctances of said shunt and said part of said magnetic circuit being such that the leakage of flux therebetween in said coil-path is substantially eliminated.

5. A magneto-electric device as defined in claim 4 but further characterized by a first of said endmembers comprising a disc extending radially outwardly from said bar, and said magnetizable shell being tubular and outwardly spaced from said disc for providing said airgap.

6. A magneto-electric device as defined in 20 1 6 claim4 but further characterized by said magnetizable shell and said shunt being tubular and substantially co-axial with said-bar.

SAMUEL EDWARD DAWSON.

REFERENCES CITED The following references'are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,830,401 Miessner Nov. 3, 1931 2,029,282 Serge Jan. 28, 1936 2,062,938 Ruppe Dec. 1, 1936 2,189,597 Wells Feb. 6, 1940 2,271,864 Honnell et a1 Feb. 3, 1942 2,286,386 -Silverman June 16, 1942 2,303,413 Washburn Dec. 1, 1942 2,307,792 Hoover Jan. 12, 1943 Petty May 9, 1944 

